Connecting smart cities with Wi-SUN

This article originally appeared in the December '21 magazine issue of Electronic Specifier Design – see ES's Magazine Archives for more featured publications.

With all this influx of residents, cities are facing increasing pressures – for example, to provide services such as water and waste, and to manage traffic and public transport. To handle the many facets of urban life, cities are turning to technology, with ‘smart cities’ using IoT devices, and ubiquitous wireless connectivity. The huge amounts of data available from various sensors and other sources can enable city planners and managers to make better decisions and to use scarce resources effectively.

It’s important to remember that the driving force behind all this technology is the quality of life for urban dwellers. The problems to be solved are complex, but solutions must always have people at their focus. This includes both the people living in an area and others who commute there to work – for bigger cities, such as London or New York, incoming workers can massively outnumber residents in some areas. Other visitors, such as tourists or attendees of events, can also benefit from smart city features, making their trip safer and more enjoyable.

For smart cities, connectivity is all-important, and networks must provide a flexible, affordable solution that provides reliable bandwidth. To address this need, in 2011, a group of companies initiated the concept of interoperable smart city networks based on the IEEE 802.15.4g standard to form the Wi-SUN (Wireless Smart Ubiquitous Network) Alliance.

The alliance now has more than 300 member companies, who are using proven industry standards to enable an open ecosystem of interoperable solutions. More than 100 million Wi-SUN devices have been deployed around the world at the time of writing. Let’s now look closer at Wi-SUN technology, and consider why it’s a good answer to the challenges of smart cities.

Wi-SUN mesh network

The Wi-SUN Field Area Network (FAN) is a robust, low-power IoT wireless mesh network. It provides scalability, security, and interoperability, and supports a large range of smart city applications. It simplifies the rollout of wireless infrastructure and can be used with both mains-powered and battery-powered devices

Most smart city applications so far have used proprietary networks, which are typically designed for specific applications with limited security and the flexibility to upgrade. They also typically use a ‘star’ architecture where devices communicate with a single base station receiver, which means they are vulnerable if the base station fails or is damaged.

Wi-SUN, on the other hand, is a self-forming, self-healing mesh network that uses thousands of nodes (rather than depending on one base station), therefore improving the system’s reliability and resilience. The Wi-SUN FAN architecture can continuously reroute data across these thousands of nodes, and this allows devices to receive full network connectivity and the continuous support of services even throughout extreme storms, cyberattacks, or general power usage constraints that can result in rolling blackouts. 

Smart city applications place tough demands on the underlying network infrastructure. Among many other elements, they require a high degree of security, reliable connections, and resilience in the event of faults/ changing conditions. Wi-SUN FAN provides secure, cost-effective and resilient connectivity with minimal additional infrastructure, from rural areas to dense urban neighbourhoods.

When compared to traditional LPWAN (Low Power Wide Area Networks), Wi-SUN offers higher data rates of up to 2.4Mb/s, and lower latency (see table below), along with low power, security and interoperability. It is based on the IPv6 protocol. Wi-SUN uses sub-GHz frequencies and the 2.4GHz band – all of which are unlicensed. The technology also allows for mode-switching techniques to adjust data rates, based on the requirements of the specific application.

Other technical advantages of Wi-SUN include better interference mitigation through frequency hopping, and the ability to cover long distances. With multiple vendors active in developing Wi-SUN products, smart city officials can ensure they’re not locked into any particular supplier and keep their options open for future developments. The open Wi-SUN standard helps promote competition – therefore keeping pricing competitive, and this ensures cities can be confident of the long-term continuity of supply.

To get started with Wi-SUN, Silicon Labs offers a Wi-SUN Wireless Starter Kit (SLWSTK6007A) with 868-915 MHz radio boards (BRD4170A). It provides all the tools needed for developing Wi-SUN wireless applications, including sensors and peripherals, and an on-board J-Link debugger.

Security as a priority

Wi-SUN’s security benefits are another differentiator. With hospitals, government agencies, public transport, business organisations and power grids becoming ever more vulnerable to cyberattacks, it’s essential that their networks are secure. Multiple cities are now interconnected, so we need to make sure they are all up to standard in their security provision.

Wi-SUN has several important built-in security functions. One of the most significant is that security authentication goes all the way back to the cloud provider, which is not typical for most other protocols. Wi-SUN also observes cybersecurity rules in designing a network to ensure reliable operations, including end-to-end security, encryption, key management, and network isolation in the event of a security breach.

A unique feature of Wi-SUN is its native public-key infrastructure (or PKI) integration, certificate-based mutual authentication, and proven data encryption and key exchange algorithms. Wi-SUN FAN access control is based on PKI and modelled after the Wi-Fi security framework. Each Wi-SUN device also has a unique certificate signed by a certification authority at its point of manufacturing.

The Wi-SUN network architecture

Lighting the way

Smart city developments today include smart metering, smart street lighting systems, public safety, traffic monitoring, noise detection and pollution monitoring. Wi-SUN FAN provides flexibility in data rates and energy consumption – enabling the efficient support of all of these applications and more. It’s also well suited to the integration of smart city sensors and distributed energy resources (or DERs) onto the grid.

One recently-established example of a Wi-SUN application is a street lighting network across the City of London. This network saw the connection of 12,000 lighting units, which replaced the city’s existing lighting stock that was reaching the end of its useful life. The new lighting reduces energy consumption and helps reduce maintenance costs.

Over the next few years, the City of London plans to add additional devices and sensors to the Wi-SUN network, including environmental monitoring. The narrow streets and tall buildings of central London pose challenges for wireless networks, which Wi-SUN handled effectively. The Wi-SUN FAN network uses multiple gateways for redundant, reliable connectivity, and increases resilience due to its self-forming and self-healing functionality.

In fact, the research firm IoT Analytics estimates that the connected streetlights market will surpass US$3.6 billion in 2023 and will grow with a CAGR of 21%. The world’s biggest implementation of connected streetlights is in Miami, with nearly 500,000 units, followed by Paris, with 280,000 connected streetlights across the city. Both these large-scale implementations use a Wi-SUN network to provide the required connectivity.

Human-centred philosophy

Wi-SUN has been built with a human-centred philosophy in mind, and its technological features allow city planners and technology architects to connect and future-proof their city’s infrastructure. Wi-SUN enables utilities, municipalities, and businesses to deploy long-range, low-power wireless mesh networks, which can connect many thousands of IoT nodes.

As smart cities develop over the coming years, Wi-SUN will provide the reliable connectivity needed to balance the priorities of sustainability and quality of life. And this will enable new applications – including those which haven’t even been thought of yet.